Volume 15, Issue 3, Pages 386-400 (September 2008) Polar Body Emission Requires a RhoA Contractile Ring and Cdc42-Mediated Membrane Protrusion  Xuan Zhang, Chunqi Ma, Ann L. Miller, Hadia Arabi Katbi, William M. Bement, X. Johné Liu  Developmental Cell  Volume 15, Issue 3, Pages 386-400 (September 2008) DOI: 10.1016/j.devcel.2008.07.005 Copyright © 2008 Elsevier Inc. Terms and Conditions

Figure 1 Cyclin B Degradation Is Required for Anaphase Initiation and for Cdc42 Activation (A) Control oocytes and oocytes injected with ΔN cyclin B1 mRNA were incubated with progesterone and withdrawn at GVBD, or 1 or 3 hr after GVBD, for MPF (histone H1 kinase) assays. GV oocytes were not treated with progesterone. Note the transient (1 hr) inactivation of MPF in control but not ΔN cyclin B1 oocytes. (B) Control oocytes and oocytes injected with ΔN cyclin B1 mRNA were treated with progesterone and fixed 3–4 hr after GVBD for chromosome analyses. Oocytes were scored as MII (metaphase II chromosome array and a polar body) or no polar body (PB). Shown are means (percentage of total oocytes examined, with SEM) of three independent experiments. The total numbers of oocytes in the three experiments are also included in the graph. Shown below are typical chromosome images of the two groups. (C) A series from a 4D movie of a control oocyte (upper row) and an oocyte injected with ΔN cyclin B1 mRNA (lower row). These oocytes were also injected with rhodamine-tubulin (red) and eGFP-wGBD (active Cdc42, green). Note the complete lack of Cdc42 activation, and lack of a polar body (PB), in oocytes injected with ΔN cyclin B1 mRNA. Scale bar is 20 μm in all images of this paper. Time (hr:min) zero corresponds to the beginning of the time-lapse experiments, typically 100–120 min after GVBD. In some oocytes, the vitelline membrane (VM) is visible with the fluorescence probes. (D) A series from a 4D movie of a control oocyte depicting dynamic localization of endogenous Aurora B (Alexa 488 anti-Aurora B, green) and microtubules (rhodamine-tubulin, red). Arrows indicate spindle midzone (MZ) or midbody (MB). Note that egg (MII) chromosomes (circle) appear much fainter (than polar body chromosomes) because they are obscured by the dense cytoplasm. (E) A series from a 4D movie of an oocyte injected with ΔN cyclin B1 mRNA depicting endogenous Aurora B (Alexa 488 anti-Aur B, green) and microtubules (rhodamine-tubulin, red). Note the attachment of intact metaphase I spindle to the oocyte cortex for an extended period of time without chromosome separation. Developmental Cell 2008 15, 386-400DOI: (10.1016/j.devcel.2008.07.005) Copyright © 2008 Elsevier Inc. Terms and Conditions

Figure 2 xSecurindm Inhibits Homolog Separation and Diminishes Cdc42 Activation (A) Control oocytes and oocytes injected with xSecurindm mRNA were incubated with progesterone and withdrawn at the indicated time for MPF assays, as in Figure 1A. (B) Control oocytes and oocytes injected with xSecurindm mRNA were treated with progesterone and fixed 3–4 h after GVBD for chromosome analyses, as in Figure 1B. Shown are means (percentage of total oocytes examined, with SEM) of three independent experiments. (C) A series from a 4D movie of an oocyte injected with xSecurindm mRNA depicting endogenous Aurora B (Alexa 488 anti-Aur B, green) and microtubules (rhodamine-tubulin, red). Note the dramatic shortening of the spindle, without polar body emission. (D) A series from a 4D movie of a control oocyte (upper row) and that of an oocyte injected with xSecurindm mRNA (lower row). These oocytes were also injected with rhodamine-tubulin (red) and eGFP-wGBD (active Cdc42, green). Cdc42 activation was diminished but not eliminated (arrow) in xSecurin dm-oocytes. Developmental Cell 2008 15, 386-400DOI: (10.1016/j.devcel.2008.07.005) Copyright © 2008 Elsevier Inc. Terms and Conditions

Figure 3 Cdc42 Activation Requires Spindle Pole Attachment to the Oocyte Cortex (A) A series from a 4D movie of an oocyte injected with C3 mRNA 60 min following GVBD to inhibit spindle rotation (Alexa 488 anti-Aur B, green; rhodamine-tubulin, red). Note the complete separation of chromosome homologs with spindle midzone clearly visible (arrows, 00:30), and the subsequent recongressing of all chromosomes. (B) A series from a 4D movie showing an oocyte injected with C3 mRNA 60 min after GVBD (eGFP-wGBD, green; rhodamine-tubulin, red). Note the complete absence of Cdc42 activation. (C) A series from a 4D movie of an oocyte injected with C3 mRNA 90 min following GVBD (eGFP-wGBD, green; rhodamine-tubulin, red). Note the limited Cdc42 activation (arrow) that did not develop into a robust cap. No polar body formed. Developmental Cell 2008 15, 386-400DOI: (10.1016/j.devcel.2008.07.005) Copyright © 2008 Elsevier Inc. Terms and Conditions

Figure 4 DN-Ect2 Inhibits RhoA Activity and Diminishes Cdc42 Activity (A) A series from a 4D movie of a control oocyte (upper row) and that of an oocyte injected with DN-Ect2 mRNA (lower row). These oocytes were also injected with eGFP-rGBD (green) and rhodamine-tubulin (red). Note the absence of RhoA contractile ring in the DN-Ect2 oocyte. (B) A series from a 4D movie of an oocyte injected with DN-Ect2 mRNA (Alexa 488 anti-Aur B, green; rhodamine-tubulin, red). Note the complete separation of chromosome homologs and the appearance of midzone Aurora B (arrows) before chromosome recongression. While the deeper chromosome set was difficult to see in some time points, the associated microtubule remnant was more evident (circle). (C) A series from a 4D movie of a control oocyte (top row), that of an oocyte injected with DN-Ect2 mRNA (middle row), and that of an oocyte injected with Cdc42N17 mRNA (bottom row). These oocytes were also injected with eGFP-wGBD (green) and rhodamine-tubulin (red). Note that Cdc42 activation was diminished but not eliminated in oocytes injected with DN-Ect2 or Cdc42N17. Developmental Cell 2008 15, 386-400DOI: (10.1016/j.devcel.2008.07.005) Copyright © 2008 Elsevier Inc. Terms and Conditions

Figure 5 Dynamic Ect2 Localization during Polar Body Emission (A) A series from a 4D movie of a control oocyte injected with rhodamine-tubulin (red) and Ect2-3GFP mRNA (green). Ect2 first appears at the central spindle and ends at the midbody. (B) A series from a 4D movie of an oocyte injected with Cdc42N17 together with rhodamine-tubulin (red) and Ect2-3GFP (green). Ect2 appears at the central spindle but fades away without contraction. (C) A series from a 4D movie of an oocyte injected with xSecurindm together with rhodamine-tubulin (red) and Ect2-3GFP (green). Ect2 signal appears more disorganized (than that in [B]) and similarly fades quickly. Developmental Cell 2008 15, 386-400DOI: (10.1016/j.devcel.2008.07.005) Copyright © 2008 Elsevier Inc. Terms and Conditions

Figure 6 Inhibition of Cdc42 Caused Hyperactivation of RhoA (A) A series from a 4D movie of a control oocyte exhibiting dynamic and complementary activity zones of RhoA (eGFP-rGBD, green) and Cdc42 (RFP-wGBD, red) during polar body (PB) formation. MB, midbody. (B) A series from a 4D movie of a Cdc42N17-injected oocyte with the same two probes as in (A). Only eGFP-rGBD signal was shown. Note that the RhoA activity zone spreads out in much larger area. Developmental Cell 2008 15, 386-400DOI: (10.1016/j.devcel.2008.07.005) Copyright © 2008 Elsevier Inc. Terms and Conditions

Figure 7 Cdc42 Templates a Dynamic F-Actin Cap Corresponding to the Forming Polar Body (A) Side view of a series from a 4D movie of a control oocyte exhibiting dynamic (d) F-actin signal (Alexa 594-G actin, red) and RhoA activity (eGFP-rGBD, green). The RhoA contractile ring had very little dynamic F-actin. (B) A single time point depicting the complete overlap between dynamic (d) F-actin (Alexa 594 G actin, red) and Cdc42 activity (eGFP-wGBD, green) during polar body emission. (C) A series from a 4D movie of a Cdc42N17-injected oocyte, with the same two probes as in (A), indicating the lack of a robust dynamic actin cap. Only residual F-actin signal was detected at the center of the robust RhoA zone, coinciding with the residual Cdc42 activity (Figure 4C, bottom row). (D) A series from a 4D movie of an oocyte exhibiting both dynamic and stable F-actin (Alexa 594 phalloidin, red) and RhoA activity (eGFP-rGBD, green). Note the significant overlap of the phalloidin probe with the RhoA contractile ring (arrows). The F-actin signal in the “roof” of the polar body (00:15, bottom row) progressively thins out during latter stage of polar body emission so the top is open, exposing the phalloidin-labeled midbody (arrow, 00:27). Developmental Cell 2008 15, 386-400DOI: (10.1016/j.devcel.2008.07.005) Copyright © 2008 Elsevier Inc. Terms and Conditions

Figure 8 RhoA Contracts Nonproductively in Cdc42N17 Oocytes (A) Top row: Side view of a series from a 4D movie of a control oocyte injected with Alexa 594-anti-Aur B and eGFP-rGBD. Note that the RhoA contractile ring constricted between the two sets of chromosomes to complete polar body (PB) emission. Middle row: Side view of a series from a 4D movie of an oocyte injected with Cdc42N17 mRNA, together with the same two probes. RhoA constricted partially, over both sets of chromosomes, resulting in failure of cytokinesis. Bottom row: Side view of a series from a 4D movie of an oocyte injected with xSecurindm mRNA, together with the same two probes. The RhoA signal appeared disorganized over the unseparated chromosomes before fading away. (B) A series from a 4D movie of an oocyte injected with RFP-Ect2 (red) together with the Rho activity probe eGFP-rGBD (green). The Ect2 ring never overlaps with the Rho contractile ring. The inset (top right) depicts an interior view of the core Ect2 ring wrapped around by the RhoA contractile ring at this time point. The dashed line marks the level of the plasma membrane (and RhoA contractile ring), and arrows indicate the levels of the Ect2 ring. The side view of this series is slightly tilted (see xyz coordinates) to show the relatively weak RFP-Ect2 signal at earlier time points. (C) A working model depicting the differential roles and regulation of Cdc42 and RhoA during female meiotic cytokinesis (side view). Cdc42 and RhoA may be activated by GEFs associated with the spindle pole (microtubule minus ends) and microtubule tips (plus ends), respectively. Cdc42 and RhoA may also functionally regulate each other (explained in the text). While the contractile ring (active RhoA and myosin II) has intrinsic contractility independent of Cdc42 function (see Figure 6B), the apparent constriction of the Ect2 ring (central spindles) is the result of Cdc42-controlled plasma membrane outpocketing, pulling the spindle upward through the constricting contractile ring. Developmental Cell 2008 15, 386-400DOI: (10.1016/j.devcel.2008.07.005) Copyright © 2008 Elsevier Inc. Terms and Conditions